1. Field of the Invention
The present invention relates to a radar apparatus mounted on a vehicle and adapted for detection of such an object as a preceding car or an obstacle around the vehicle and, more particularly, to an on-vehicle DBF radar apparatus arranged to detect the object by scanning with radar beams synthesized by digital signal processing.
2. Related Background Art
Since the DBF (digital beamforming) radar apparatus synthesizing the radar beams by digital signal processing needs to have no scanning mechanism, it can be designed readily in compact and lightweight structure and it is resistant to the negative effect of vibration. Therefore, it is expected to be used as a radar apparatus for on-vehicle use.
In the conventional DBF radar apparatus popularly employed, a scanning range and an effective detection distance were preset and the radar beams swept an entire detection range determined by the scanning range and effective detection distance.
Incidentally, the radar beam scanning in the DBF radar apparatus was actually achieved in such a way that the scanning range was divided into plural directions and a radar beam was synthesized in each of the divided directions. Therefore, the synthesis operation of radar beam was carried out the number of division times in one scanning.
This posed the problem that as the scanning resolution was enhanced, the operation amount for the synthesis of radar beams became larger, so as to lengthen the operation time and this resulted in delay in acquisition of object detection information.
In contrast with it, if the operation amount was decreased by lowering the scanning resolution of radar beams, the time necessary for one scanning could be reduced, but the target detection accuracy would be degraded.
An on-vehicle DBF radar apparatus of the present invention has been accomplished in order to solve the above problems and is characterized by comprising lane shape acquiring means for acquiring a shape of a lane on which a vehicle is driving and by limiting a scanning range of radar beams according to the shape of the lane acquired by the lane shape acquiring means.
A target to be detected by the on-vehicle radar apparatus is normally an object on a driving road including a driving lane, either a preceding car or an obstacle. In other words, any object present in areas except for the driving road can normally be regarded as an object not to be detected.
According to the present invention, because the scanning range is limited according to the lane shape, the areas except for the driving road can be set as non-scanned areas while the driving road is maintained in the scanning range. In this case, because the scanning range becomes narrower, the processing time necessary for the radar beam scanning can be decreased without degradation of the scanning resolution.
The scanning range is desirably made to differ according to a target distance for object detection. Assuming that the width of the driving road is constant, angles subtending the width of the driving road become narrower with increasing distance; therefore, the shape of the detection range can be approximated to the shape of the driving road by narrowing the scanning range with increasing distance.
In that case, the center of the scanning range desirably varies according to the shape of the driving road, i.e., varies along the shape of the lane detected.
This permits the detection range to be narrowed into a necessary and sufficient region, whereby the processing time can be decreased more.
One of the lane shape acquiring means is lane curvature detecting means for detecting a degree of curvature of the lane. The curvature of lane can be calculated from a vehicle velocity and a yaw rate. Vehicle velocity detecting means or yaw rate detecting means is often mounted on vehicles for the other purposes and thus a dedicated sensor does not have to be prepared when the detection result of these means is used to obtain the curvature of lane.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.